This invention relates to a total artificial heart prosthesis capable of fully replacing a natural heart to perform the cardiac function.
Currently known are various embodiments of total artificial hearts which are formed from biologically inert plastic materials and metals, the same differring in their principles of operation and actuating means employed. Since the first experiments with artificial hearts in 1957, many improvements have been introduced and increasingly more sophisticated approaches have been proposed. The interest in total artificial hearts is also justified by that, contrary to heart transplants which require the availability of such organs and involve well-kown rejection problems, total artificial hearts are suitable for mass production and can, therefore, be made available to a much higher number of patients.
The requisites for an artificial heart prosthesis are: a limited size, on the same order as the human heart; extremely high reliability of operation; prolonged operation capabilities; delivery "flexibility", or capability to supply each time a sufficient delivery to support the entire organism as its demands vary; capability to pump the blood in a gentle manner to avoid hemolysis, i.e. destruction of the red cells; independence of bulky power sources which are difficult to carry around.
The various approaches which are presently known exhibit at least one or more of the main deficiencies listed above, and the need for novel approaches which can obviate them is, therefore, much felt.
In a first artificial heart, blood was pumped by deformation of an elastic membrane, which was driven by compressed air from an external source. That source was fairly bulky and delivery to meet the body demand was complicated to adjust.
A further embodiment employed computer monitoring to control said delivery. Also experimented was a nuclear powered heart, wherein heat was utilized to drive a thermocompressive motor which, through either a pneumatic, or hydraulic, or mechanical system, drove in turn a blood pump. Both attempts enjoyed but limited success, because the devices were complex, bulky, and expensive. It has never been possible to keep laboratory animals alive with them for more than two days.
Additional disadvantages were their liability to mechanical failure, difficulty of insertion with a propensity for obstruction of the venous flow through the right atrium, and excessive hemolysis.
In spite of subsequent improvement with the diaphragm-type pumping element, which improved both the mechanical reliability and hemolysis, extending survival of the laboratory animals up to two weeks, even this embodiment had the disadvantage of forming clots, with attendant internal hemorrhage that could not be checked.
At the present time, the most perfected of artificial hearts is the Jarvik-7 heart, which has polyurethane ventricles supported on aluminum receptacles and tilting disk valves. It succeeded in keeping alive the animals for a period of several months. A calf equipped with such a heart was brought over seven months from a weight of ninety kilograms at the time of the surgical intervention up to above 160 kilograms.
In view of the improvement achieved in the blood handling mechanism, the attention is now focused on improving the power, in particular electric power, converters. Studies are being carried out which are directed toward the realization of an electro-hydraulic power converter having a single moving part and being battery powered. By reversing the direction of rotation of a pump associated with a DC motor, the direction of the hydraulic flow (low-viscosity silicone oil operating a diaphragm similarly to compressed air) is inverted. The hydraulic fluid is pumped back-and-forth between the right and left ventricles, thereby downtime for motion reversal becomes unavoidable.